This invention relates to an exposure method and a scanning exposure apparatus using the same. The present invention is suitably usable, for example, for photoprinting a photomask pattern (reticle pattern) illuminated with slit-like light on a wafer while synchronously scanning the photomask and the wafer relative to the slit-like light and a projection optical system, for the manufacture of a semiconductor device such as an IC or LSI, an image pickup device such as a CCD, a display device such as a liquid crystal panel, or a device such as a magnetic head, for example.
The semiconductor device manufacturing technology has advanced remarkably, and the microprocessing technology has also advanced notably. Particularly, as regards reduction projection exposure apparatuses having a resolving power of submicron order, which play a major role in the optical processing technology, enlargement of a numerical aperture (NA) and shortening of exposure wavelength have been attempted, for further improvement of the resolution.
Also, changing a unit-magnification scanning exposure apparatus using a conventional reflection projection optical system has been proposed. That is, there is a scanning exposure apparatus which includes a reduction projection optical system comprising a combination of reflective and refractive optical elements (catadioptric system), or a reduction projection optical system comprising refractive elements only, wherein a mask stage for a photomask and a wafer stage for a photosensitive substrate are scanningly moved in synchronism with each other and at a speed ratio corresponding to the reduction magnification.
FIG. 8 is a schematic view of a main portion of such a scanning exposure apparatus of a step-and-scan type. In the drawing, a mask 1 has a device pattern (original pattern) 21 formed thereon, and it is supported by a mask stage 4. A wafer (photosensitive substrate) 3 is supported by a wafer stage 5. The mask 1 and the wafer 3 are disposed at positions being optically conjugate with each other with respect to a projection optical system 2. Slit-like exposure light 6 being elongated in the Y direction in the drawing is supplied from an illumination system (not shown), and it illuminates the mask 1. Then, the pattern of the mask 1 as illuminated is imaged upon the wafer 3, at a size determined by the projection magnification of the projection optical system 2.
The scan exposure is accomplished by moving, through a driving unit, the mask stage 4 and the wafer stage 5 relative to the slit-like exposure light 6 and the projection optical system 2, in the X direction and at a speed ratio corresponding to the optical magnification. Thus, by scanning the mask 1 and the wafer 3 relative to the exposure light 6 and the projection optical system 2, the whole device pattern 21 of the mask 1 is transferred to a transfer region on the wafer 3.
In the scanning exposure apparatus based on the step-and-scan exposure method, when the scan exposure of one shot (31) upon the wafer 3 is completed, the wafer stage 5 carrying the wafer 3 thereon is moved by a predetermined amount, and the scan exposure of a next shot on the wafer is then carried out. This operation is repeated to perform exposures of the whole wafer.
In such a scanning exposure apparatus, since the exposure region has a rectangular or slit-like shape, the lens elements of the projection optical system 2 are illuminated with light of a rectangular shape or of an elliptical shape (the slit-like shape is expanded in accordance with an extension of the illumination light flux), the shape being determined at the location where the lens element is placed. This means that the rectangular or slit-like region of each lens element is heated by the light.
As the exposure procedure goes on, such a heating environment may cause revolutionally asymmetric deformation of the projection lens and produce a revolutionally asymmetric aberration. For example, an astigmatism aberration may be caused in the light being imaged on the wafer 3, which may largely degrade a device pattern image thereon.
This tendency becomes notable as the printing wavelength is shortened from i-line (365 nm) to a deep ultraviolet region (248 nm or 193 nm), because, in physical properties, the light is absorbed more by the glass material.
Japanese Laid-Open Patent Application, Laid-Open No. 50585/1998 proposes a solution for this problem.
It is an object of the present invention to provide an exposure method and a scanning exposure apparatus using the same, by which production of a revolutionally asymmetric aberration such as described above can be reduced effectively, in a different way than as proposed in the aforementioned Japanese patent application.
In accordance with an aspect of the present invention, there is provided an exposure method wherein a first object is illuminated with a slit-like light beam while the first object and a second object are scanningly moved at a speed ratio corresponding to a projection magnification of a projection optical system such that a pattern of the first object is projected onto the second object through the projection optical system, characterized by illuminating a mark provided on the first object side with exposure. light, wherein light from the mark is incident on the projection optical system whereby a revolutionally asymmetric aberration of the projection optical system due to an exposure is corrected or reduced.
In accordance with another aspect of the present invention, there is provided an exposure method wherein a first object is illuminated with a slit-like light beam while the first object and a second object are scanningly moved at a speed ratio corresponding to a projection magnification of a projection optical system such that a pattern of the first object is projected onto the second object through the projection optical system, characterized by illuminating a mark provided on a stage for the first object, wherein light from the mark is incident on the projection optical system whereby a revolutionally asymmetric aberration of the projection optical system due to an exposure is corrected or reduced.
In accordance with a further aspect of the present invention, there is provided an exposure method wherein a first object is illuminated with a slit-like light beam while the first object and a second object are scanningly moved at a speed ratio corresponding to a projection magnification of a projection optical system such that a pattern of the first object is projected onto the second object through the projection optical system, characterized by illuminating a mark provided on the first object side with exposure light, wherein light from the mark is incident on the projection optical system whereby at least one lens of the projection optical system is substantially thermally saturated.
In accordance with a yet further aspect of the present invention, there is provided an exposure method wherein a first object is illuminated with a slit-like light beam while the first object and a second object are scanningly moved at a speed ratio corresponding to a projection magnification of a projection optical system such that a pattern of the first object is projected onto the second object through the projection optical system, characterized by illuminating a mark provided on a stage for the first object, wherein light from the mark is incident on the projection optical system whereby at least one lens of the projection optical system is substantially thermally saturated.
In accordance with a still further aspect of the present invention, there is provided an exposure method for projecting a pattern of a first object onto a second object through a projection optical system, characterized by illuminating a mark provided on the first object side with exposure light, wherein light from the mark is incident on the projection optical system whereby a revolutionally asymmetric aberration of the projection optical system due to an exposure is corrected or reduced.
In accordance with another aspect of the present invention, there is provided an exposure method for projecting a pattern of a first object onto a second object through a projection optical system, characterized by illuminating a mark provided on a stage for the first object with exposure light, wherein light from the mark is incident on the projection optical system whereby a revolutionally asymmetric aberration of the projection optical system due to an exposure is corrected or reduced.
In accordance with a yet further aspect of the present invention, there is provided an exposure method for projecting a pattern of a first object onto a second object through a projection optical system, characterized by illuminating a mark provided on the first object side with exposure light, wherein light from the mark is incident on the projection optical system whereby at least one lens of the projection optical system is substantially thermally saturated.
In accordance with a further aspect of the present invention, there is provided an exposure method for projecting a pattern of a first object onto a second object through a projection optical system, characterized by illuminating a mark provided on a stage for the first object, wherein light from the mark is incident on the projection optical system whereby at least one lens of the projection optical system is substantially thermally saturated.
In these aspects of the present invention, the illumination of the mark on the first object side may be performed before a regular shot exposure to the wafer and/or between shot exposures to the wafer.
The mark may be provided on a movable stage on which the first object is placed.
The mark may comprise a light diverging element for producing light which is revolutionally asymmetric with respect to an optical axis of the projection optical system.
The mark may comprise a light diverging element for diffusing light incident thereon, mainly along a scan direction.
The light from the mark may be incident on a region of the projection optical system, which region is revolutionally symmetric with respect to an optical axis thereof.
The light from the mark may be incident on a complementary region, for an irradiation region on a lens of the projection optical system for exposure of a shot of the second object.
The first object may be illuminated with a slit-like light effective to define an illumination region of rectangular or arcuate shape on the first object.
The projection optical system may include plural lenses.
In accordance with a yet further aspect of the present invention, there is provided a scanning exposure apparatus for performing an exposure process in accordance with an exposure method as recited above.
In accordance with a yet further aspect of the present invention, there is provided an exposure apparatus for performing an exposure process in accordance with an exposure method as recited above.
In accordance with a still further aspect of the present invention, there is provided a device manufacturing method for exposing a wafer to a device pattern by use of an exposure method as recited above, and for developing the exposed wafer.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.